The subject matter disclosed herein relates to biomass gasification systems and, more specifically, to the removal and processing of tar from producer gas generated by the system.
In biomass gasification processes, a solid fuel such as sawdust, agricultural wastes, wood wastes, and the like, is gasified to generate a gaseous fuel. The biomass generally includes polysaccharides that have been produced by photosynthesis, such as cellulose, hemicellulose, and lignin. During the gasification of these materials, the biomass, in the presence of air, is converted into a more combustible form, referred to as producer gas. In some systems, the producer gas may be combusted by an engine to produce electricity. In other systems, the producer gas may be used to generate heat or to generate substitute natural gas (SNG).
The producer gas includes combustible gases such as carbon monoxide (CO), hydrogen (H2), and methane (CH4), among others. In addition to producing the combustible gases noted above, the biomass gasification process also produces significant amounts of tar compared to other gasification processes. The tar may include molecules having a molecular weight higher than benzene (C6H6), including aromatic hydrocarbons, polyaromatic hydrocarbons (PAH's), heterocyclic aromatics, and the like. While certain tars may not have a substantial effect on the operation of a power plant having the biomass gasification system, other tars may condense and/or crystallize within certain equipment, thereby causing a reduction in plant efficiency and, in some situations, plant downtime.